[PATCH v2] arm: Fix backtrace generation when IPI is masked

On Tue, Sep 15, 2015 at 02:15:10PM +0100, Daniel Thompson wrote:

Actually it already gets masked out. The argument to raise_nmi() points to a
data structure owned by the backtrace library functions and this structure
if altered during the execution of nmi_cpu_backtrace() to clear the calling
CPU.

I had originally planned to use cpumask_test_and_clear_cpu() for the
conditional branch but that would be broken because nmi_cpu_backtrace()
would become a nop if we clear anything from the mask before calling it!

I guess I should add a comment about this to save us from broken but
"obviously correct" cleanups in the future...

Absolutely.

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